Out-of-Plane Web Deformation and Relative Arch Movement of Hybrid-Composite Beams Based on Photogrammetry

Recently invented by John R. Hillman, Hybrid-Composite Beams (HCBs) are a new approach to structural design that incorporate four materials in such a way as to maximize the efficiency of each material. A concrete arch serves as the main compression reinforcement, with steel strands tying the arch and carrying tension forces. The space between the arch and the steel is filled with stiff, lightweight foam. A Fiber Reinforced Plastic (FRP) box encases the system and adds shear reinforcement. The Virginia Department of Transportation is interested in using HCBs in bridges and funded a project at Virginia Tech to better understand the behavior of the beams.

Close-range photogrammetry was incorporated into the project to detect out-of-plane movement of the FRP web and movement of the arch within the FRP shell due to applied loads. The individual beam underwent two phases of testing, the first of which occurred prior to the concrete arch being placed in the beam. The second phase took place after the arch cured. A total of 22 photosets were taken of the beam, four during Phase I and 18 during Phase II.

The results of the FRP web study indicate that beam is flexible laterally and prone to lateral displacement when not connected to a larger bridge system. Significant movement of the arch within the FRP shell was detected demonstrating sinusoidal behavior along the edge of the arch and restrained movement at the center of the arch.